Cation distortion isomerism in three five-co-ordinate diethylenetriamine(di-2-pyridylamine)copper(II) complexes

Abstract

The crystal structures of three [Cu(dien)(bipyam)]X₂·nH₂O (dien = diethylenetriamine, bipyam = di-2-pyridylamine) complexes have been determined by X-ray crystallographic methods, where X = Cl^–, n= 2 (1); X = ClO₄^–, n= 1 (2); and X = NO₃^–, n= 0 (3). All three crystallise in the monoclinic space group P2₁/c with Z= 4; in (1)a= 7.78(2), b= 9.75(3), c= 28.01(5)Å, and β= 115.0(5)°; in (2)a= 15.683(5), b= 7.621(5), c= 21.044(9)Å, and β= 121.42(2)°; and in (3)a= 12.201(5), b= 16.052(6), c= 9.851(4)Å, and β= 90.76(2)°. All three structures were solved by heavy-atom techniques and successive Fourier syntheses; all three complexes involve a distorted five-co-ordinate CuN₅ chromophore, whose stereochemistry ranges from distorted square pyramidal in (1), through an intermediate geometry in (2), to a distorted trigonal-bipyramidal stereochemistry in (3). The three stereochemistries represent individual structures in the pathway of the Berry twist and represent cation distortion isomers of the [Cu(dien)(bipyam)]²⁺ cation. The angular changes in the CuN₅ stereochemistry are parallelled in the electronic reflectance spectra of the three complexes and in the calculated crystal-field energy level of the copper(II) ion.